Step wave generators



March 20, 1956 w. D. HOUGHTON 2,739,234

STEP WAVE GENERATORS Filed Feb. 27, 1951 5 Sheets-Sheet l lNV NTORATTORNEY March 20, 1956 W. D. HOUG HTON STEP WAVE GENERATORS 5Sheets-Sheet 2 Filed Feb. 27, 1951 March 20, 1956 w 5, HQUGHTON2,739,234

STEP WAVE GENERATORS i lNPiT L'UU/WZ-"BI i0 T *3 I --\----fi/ w g? T i i604 7?! gig-55%] I]; I 50 g 10 1'0 J J L a w mil? j/i Z6 75 077 117MEL/( ATTORNEY United States Patent STEP WAVE GENERATORS William D.Houghton, Princeton, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application February 27, 1951, Serial No.212,909

The terminal fifteen years of the term of the patent to be granted hasbeen disclaimed 16 Claims. (Cl. 25027) This invention relates to stepvoltage wave generators.

A step voltage wave may be defined as a Wave produced by adding in timesequence incremental voltages and maintaining the resultant voltagebetween the times of such addition. After the addition of apredetermined number of such increments, the voltage rapidly decreasesto a low value whence the process is repeated. The wave thus consists ofa series of cycles of changing voltage in which each cycle, when plottedwith time as abscissa and amplitude as ordinate has the shape of theprofile of a set of steps. Since some finite time is required to add theincremental voltages, the risers which connect the steps are not exactlyperpendicular. However, the riser time is made quite small relative tothe time between additions.

Step wave generators find many applications in present day electronicapparatus. By way of example, by means of difierently biased amplifiersarranged to become sequentially operative with the application ofdifferent voltages applied to their inputs, a step voltage wave may beused to switch on and off the amplifiers in a desired sequence. Such anarrangement is known as an electronic switching or commutating devicewhich finds utility in multiplex communications systems.

in order to add and store the incremental voltage changes or steps, itis common practice to use a condenser as a storage element. However, thevoltage charge which is induced in a condenser by voltage changes ofequal amplitude and time duration is not linear. That is, in thedischarged state of the condenser, the application of a particularvoltage for a given time period will result in a voltage increase whichis greater than that resulting from the application of the sameamplitude voltage for the same period at a time when the condenser ismore fully charged. In other words, due to the exponential charging rateof a condenser, the application of equal amplitudes of voltage for equaltimes results in gradually decreasing voltage changes in the storedvoltage.

Accordingly, it is an object of this invention to provide a novel methodof and means for generating a step voltage wave having equal incrementalincreases between steps constituting the step voltage wave.

Another object of the invention is to provide an improved step voltagewave generator in which the individual voltage changes of the generatedwave have a predetermined amplitude range.

Still another object of the invention is the provision of a novelgenerator of step voltage waves the steps of which do not follow thecharging rate of a storage device such as a condenser.

In accordance with the invention, the above and other objects areachieved by the provision of means for charging a storage condenserthrough a vacuum tube and varying the effective impedance of thecharging tube in accordance with the degree of charge of the storagecondenser. The variation in effective impedance is obtained by means ofa compensating condenser connected in the anode circuit of the chargingtube. The compensating condenser is charged during the step wave cycleand effectively increases the anode potential of the charging tube andhence its effective impedance. The storage condenser and compensatingcondenser are simultaneously discharged at the end of the step wavecycle.

The invention will be clear by reference to the following detaileddescription taken in conjunction with the accompanying, drawings inwhich:

Figs. la through 1 illustrate the principles of the invention; 1

Fig. 2 representsschematically an embodiment of the invention;

Fig. 3 represents schematically a modification of the circuitarrangement of Fig. 2; V

Fig. 4 represents schematically a modified form of s the invention; t

Fig. 5 represents schematically a modification of the arrangement shownin Fig. 4; and v Fig. 6 represents schematically still anothermodification of the circuit arrangement of Fig. 2.

Referring to Fig. 1a there is shown an assumed curve, in solid lines,representing two cycles of a step voltage wave such as would be producedby charging a condenser with equal time duration pulses of equalamplitude voltages and discharging the stored voltage after apredetermined number of pulses. For purposes of simplicity, only threesteps have been illustrated. It is to be understood that the principlesof the invention are applicable to similar arrangements producing anydesired number of steps. It will be noted, that the voltage risers ofthe steps are not uniform but decrease with increase in stored voltageas indicated by the dotted line y. The dotted line y, as explainedabove, corresponds to the exponential charging rate of the storagecondenser.

In Fig. 1b there is shown an idealized curve, in solid lines,representing two cycles of a step voltage wave the risers of the stepsof which are equal in amplitude, as indicated by the dotted line x. Thehatched portions under the last two steps indicate the additional chargenecessary to arrive at the linear increase in stored voltage.

From an inspection of Fig. la it will be clear that in the absence ofextremely sensitive apparatus, the voltage change in the last step is sosmall as to make its use impractical. Thus, although a three step wavehas been generated, its practical use is limited to two steps. However,by providing the equal riser step voltage wave of Fig. lb all steps maybe used.

Referring now to Fig. 2, there is shown an embodiment of the inventionapplied to a common type of step wave generator. In order to simplifythe description of the invention, that portion of the circuitry of Fig.2 which has been added in accordance with the invention is enclosedwithin the dotted box 23a.

In this figure, the pulse generator consists of a crystal controlledoscillator comprising a vacuum tube 18 provided with a crystal 10,tuning condensers 12 and 13, a grid blocking condenser 11, a grid leak14, and an anode resistor 17 as shown. A transformer 16 is coupledbetween the cathode of the tube 18 and ground, and across the cathoderesistor 15. The tube 18 conducts on each positive peak of the sine wavedeveloped across its grid and, hence, pulses of anode current flowtherethrough. Any type of pulse generator may be used, the particulararrangement shown being merely for the purpose of illustration.

The pulses of anode current result in pulses of voltage being developedacross the primary winding of the transformer 16. The windings on thetransformer 16 are so poled that a positive pulse is developed acrossthe resistor 20 connected between the grid and cathode of a vacuum tube23. Each pulse developed across the resistor 20 is made suflicient inamplitude to drive the tube 23 to a positive grid-to-cathode potentialcausing electron current to flow in the grid circuit of tube 23 andhence store a charge in condenser 19. After the pulse across theresistor 20 has ceased, the charge stored in condenser 19 leaks 011through resistor 20 and develops a bias thereacross sutiicient tomaintain the tube23 below cut off for the time interval between appliedpulses.

Disregarding for the moment, the eflect of the elements Within thedotted box 23a it will be seen that each time the tube 23 conducts,current flows into condenser 21 storing a charge therein. Since there isno resistance across condenser 21, the charge stored by each pulse isadded to the charges stored by the preceding pulses. This results insteps of voltage as shown in Fig. la being developed across condenser 21and also between the grid of a vacuum tube 25 and ground. The tube 25 isnormally biased below cut oil? due to bias developed across its cathoderesistor 26. When the voltage on the grid of tube 25 exceeds the bias onits cathode, anode current starts toflow in the anode winding B oftransformer 24. The windings a and b of transformer 24 are so poled thatan increase in current in winding b causes an increase in voltage on thegrid of tube 25. The increased grid voltage further increases the anodecurrent which in turn further increases the grid voltage. This actioncontinues until the grid of tube 25 draws grid current. The grid currentfrom tube 25 then discharges condenser 21. When grid current starts toflow in the grid of tube 25, the anode current ceases to increase whichresults in a decrease in grid voltage. The decrease in grid voltagecauses a reduction in anode current. This action continues until tube 25cuts off. During the time when tube 25 conducts, a charge is stored incondenser 27, and when tube 25 cuts ofi the charge stored in condenser27 leaks off through resistor 26. Resistor 26 is chosen to be of such avalue that a direct current voltage of the desired magnitude isdeveloped thereacross. The magnitude of the bias voltage developedacross resistor 26 is made slightly greater than the peak to peakamplitude of the step voltage wave developed across the condenser 21.

- Tube 29 is a cathode follower which faithfully passes a waveformrepresentative of the step wave voltage devel- 4 constant and thereforeall risers in the step voltage wave will be of practically equalamplitude.

By properly proportioning the values of resistor 22 and condenser 30,over-compensation may be achieved. That is, the upper risers may be madelarger than the lower risers. In addition the parameters of resistor 22and condenser 30 may be designed to cause larger risers in the centerthan at the upper or lower ends. As an example of one arrangement whichhas proved satisfactory to give equal risers with 280 volts applied tothe positive terminal the components were given the following values:

Resistor 22 ohms 100,000 Resistor 20 megohm l Condenser 19 "mi... .01Condenser 21 mmf 330 Condenser 3t mf .001

in Fig. 3 there is shown a modification of the arrangement of Fig. 2 inwhich the positive potential end of the winding B of transformer 24 isreturned to the anode of tube 23 and also to the junction betweenresistor 22 and condenser 39. This arrangement makes possible theelimination of the tube 50. In this case the anode current of the tube25 is used to discharge the condenser 30 so that it may perform, itscompensating action. The remainder of the circuitry acts as describedfor the arrangement shown in Fig. 2.

In Fig. 4 there is shown an arrangement providing a compensated stepvoltage wave in which the discharge of the storage capacitor 21 and thecompensating condenser 30 is obtained by an external control pulse. Inthat figure, a step voltage wave is developed across the condenser 21 asdescribed in connection with the arrangement shown in Fig. 2. It will benoted that the input control pulses are also supplied to an electroniccounter circuit indicated by the box 60. The counter circuit may be ofany suitable type. One common type of counter is the usual step wavegenerator since, after a predeteroped across condenser 21, forutilization at output terminals 70 and 71.

It will now be seen that without compensation the impedance of tube 23increases as the amplitude of the step voltage across condenser 21increases due to the fact that each time the voltage across thecondenser 21 is increased the effective anode potential of tube 23 isdecreased by an amount representative of the charge stored in condenser21. This results in a further non-linearity between the lower and uppervoltage risers of the step wave.

Considering now the eifect of the addition of the vacuum tube and thecondenser 30 to the circuit so far described, it will be seen that eachtime the voltage on the grid of tube 25 rises to a point where tube 25conducts, tube 50 will also conduct since their grids are connected inan electrically parallel manner as shown. The grid current from tube 25causes condenser 21 to be discharged as previously described. When tube50 conducts it causes condenser 30 to be discharged. During the cut offtime of tubes 25 and 50, condenser 30 charges linearly through resistor22 with a resulting wave form as shown in Fig. lc. The smallirregularities in the wave form of Fig. 1c are slight discharges ofcondenser 30 due to tube 23 becoming conducting at the pulse time.

it will be seen that as the voltage across condenser 21 increases, thevoltage applied to the anode of tube 23 also increases due to the chargestored in condenser 30. As a result, the charge stored in condenser 21due to tube 23 being made conducting may be made practically minednumber of input pulses an output pulse is generated. Thus an arrangementsuch as shown in Fig. 2 where the input pulses are derived from theinput to the circuit arrangement of Fig. 3 instead of the oscillatormaybe used. Since only the output pulse isrequired, the bitcuit need not becompensated. However, in accordance with the invention, the compensatingcondenser 30 and the tube 50 may be made common to all the step wavegenerators and all may be thus compensated. After a predetermined numberof input pulses, the counter 60 produces a pulse. This pulse is coupledto the grids of the normally non-conducting vacuum tubes 63 and 64, andcauses them to become conducting. Tubes 63 and 64 are normally biased tocut oil by means of a suitable bias source Ec- The tube 64 dischargesthe storage condenser 21 and thus,

completes a cycle of step wave generation. Tube 63 discharges condenser30. The operation of the remainder of the circuit is the same asdescribed in connection with the circuit arrangement of Fig. 2.

The arrangement illustrated in Fig. 5 is similar to that shown in Fig. 4with the exception that separate inputs are provided for the dischargetubes 63 and 64. The input to tube 63 is in the form of a square wavepulse which is synchronous with the step wave. The square wave pulse maybe derived from any suitable source such, by way of example, as thesimple multivibrators or relaxation oscillators described by Eugene R.Shenk in the January, February and March 1944 issues of the publicationElectronics.

When a square wave pulse such as illustrated in Fig. 1d

is applied to the input of tube 63 it will be conducting for one-half ofthe step wave cycle and non-conducting for the remainder of the cycle.During its conducting time the compensatingcondenser 30 will remain discharged and hence no compensation will'be provided.

During its non-conducting time the condenser 30 will charge at aconstant rate and compensation will be provided in the manner alreadydescribed. The charge cycle of condenser 30 under these conditions isillustrated in Fig; 1e. The resulting step wave is illustrated in Fig. 1It will be seen that over-compensation is provided for the later steps.

It will be clear, that, by providing a suitably shaped input wave tocontrol the on-ofi operating times of tube 63, a desired amount ofcompensation may be provided over the entire step wave cycle.

The arrangement shown in Fig. 6 is similar to that shown in Fig. 2 withthe exception of certain changes in the transformer 24 and itsconnections. Each time tube 25 conducts as described above, a positivepulse is developed across the winding C of the transformer 24. Thepositive pulses thus developed are applied to the grid of tube 50 andcondenser discharges in a manner already described. The voltage storedin condenser 21 is applied to the grid of tube 25 through winding A oftransformer 24. The discharge of storage condenser 21 is eitected bytube 25 in a manner already described.

What I claim is:

l. A wave generator comprising in combination an electron device havinga cathode electrode and an anode electrode, a storage device connectedbetween said cathode and a point of fixed reference potential, means forapplying a charging potential between said anode and said point of fixedreference potential in the form of equal amplitude and time durationpulses, a second storage device connected between said anode and saidpoint of fixed reference potential, a second electron device connectedin parallel with said second storage device, a third electron deviceconnected to said first mentioned storage device and controlled thereby,and means whereby said second and third electron devices are madeconducting after a predetermined number of said pulses.

2. A wave generator according to claim 1 including means to render saidsecond and third electron devices simultaneously and momentarilyconducting at the end of each wave cycle.

3. A wave generator according to claim 1 including means whereby theconduction times of said second and third electron devices may beindependently controlled.

4. A wave generator comprising in combination an electron device havinga cathode, a grid, and an anode, a resistance connected between saidgrid and said cathode, a resistance connected between said anode and apotential supply source terminal, a storage device connected betweensaid cathode and a point of fixed reference potential, means coupled tosaid electron device for applying control pulses to said grid wherebysaid electron device is conducting only during the duration of saidpulses, a second electron device having a grid electrode and an anode,means coupling said storage device and said grid electrode fordischarging said storage device through said grid electrode, a secondstorage device connected between said anode of said first mentionedelectron device and said point of fixed reference potential, meanscoupling said second storage device and said anode of said secondelectron device for discharging said second storage device through anodeof said second electron device, and means coupled to said secondelectron device for controlling the conduction time of said secondelectron device whereby said storage devices are discharged only afterthe occurrence of a predetermined number of said pulses.

5. A wave generator comprising in combination, a first vacuum tubehaving a cathode, a control grid and an anode, a first storage condenserconnected between said cathode and ground, a resistance connectedbetween said grid and said cathode, a resistance connected between saidanode and a potential supply source terminal, means coupled to said gridfor applying control pulses thereto whereby said tube is conducting onlyduring the duration of said pulses, a second storage device connectedbetween said anode and ground, and means coupled to said storage devicefor cyclically discharging said storage devices.

6. A wave generator according to claim 5 wherein said last mentionedmeans includes a second vacuum tube having a cathode, an anode and acontrol grid, said anode of said second tube being coupled to said anodeof said first tube, said cathode of said second tube being connected toground, and means for supplying control po tential pulses tosaid controlgrid of saidsecond tube to control its conduction time and hence thedischarge of said second storage device. V

7. A wave generator according to claim 6' including means to couple thecontrol grid of said second tube to said first storage device wherebysaid first storage device is discharged by means of grid current llowduring said conduction time.

8. A wave generator according to claim 6 including a third vacuum tubecoupled to said first storage device to discharge said first storagedevice.

9. A wave generator according to claim 6 including means coupled to saidsecond and third tubes to apply the same source of potential pulses toboth said second and said third tubes to control the time of conductionof both said second and said third tubes.

10. A wave generator according to claim 6 including means coupledbetween said first storage device and said second and third tubes toapply the potential stored in said first storage device to the controlelectrodes of said second and third tubes to control the conduction timeof both said second and said third tubes.

11. A Wave generator according to claim 8 including a separate source ofcontrol pulses coupled to said second and third tubes to simultaneouslycontrol their times of conduction.

12. A circuit arrangement for cumulating a charge on a storage device insubstantially equal increments, including an electron discharge devicehaving at least a cathode.

electrode and an anode electrode defining a space charge path connectedin series circuit with said storage device, a further storage deviceconnected across said series circuit, and an electron dischargestructure having at least an anode and a cathode defining a space chargepath connected across said further storage device and having a trondischarge device and a point of fixed reference potential, means toapply recurrent charging potentials of substantially constant amplitudeto said electron discharge device whereby said storage device is chargedin successively decreasing increments, a further storage device coupledin circuit between said anode electrode and said point of fixedreference potential, an electron discharge structure having at least ananode connected to said anode electrode, a cathode coupled to said pointof fixed reference potential and a control grid, and means coupling saidcontrol grid to said cathode electrode of said electron dischargedevice, thereby to vary the effective impedance of said electrondischarge device to compen sate at least in part for the decreasingincrement of the charge stored in the first said storage device.

14. A circuit arrangement for cumulating a charge on a storage device insubstantially equal increments, including an electron discharge devicehaving at least a cathode electrode, a control electrode, and an anodeelectrode defining a space charge path connected in series circuit withsaid storage device, a resistance connected between said controlelectrode and said cathode electrode, a resistance connected betweensaid anode electrode and a potential supply source terminal, meanscoupled to said control electrode for applying control pulses theretowhereby said electron discharge device is conducting only during theduration of said pulses, a furthe: storage device connected across saidseries circuit, anelectron discharge structure having at least a grid,an

anodeand a cathode defining a space charge path conne ctedv across saidfurther storage device, and a normally blocked electron discharge tube.circuit coupled between said grid and the junction between said electrodischarge device and said first storage device.

15. A circuit arrangement for cumulating a charge on' a capacitor inequal increments, including an electron discharge device having at leasta cathode electrode, a grid electrode and an anode electrode, saidcapacitor oeing connected between the cathode electrode of said electrondischarge device and a point of fixed reference potential, a resistanceconnected between said anode electrode and apotentialsuppl'y sourceterminal, a resistance connected between said grid and cathodeelectrodes, means coupled to said grid electrode to apply recurrentcharging potentials of substantially constant amplitude thereto wherebysaid electron discharge device is con ducting only during the durationof said recurrent potentials so that said capacitor is charged insuccessively decreasing increments, a further capacitor coupled in circuit between said anode electrode and said point of fixed referencepotential, an electron discharge structure having at least an anodeconnected to said anode electrode, a cathode coupled to said point offixed reference potential and a control grid, and a normally blockedelectron discharge tube circuit coupling said control grid to saidcathode electrode ofg said electron discharge device,

the conduction time of said secondtube in response to theapplicationthereto of pulses developed by said third tube,

References Cited in the file of this patent UNITED STATES PATENTS21,10,015 Fitzgerald Mar. 1, 1938 2,122,464 Gol'ay. July 5, 19332,195,996 Palmer Apr. 2, 1940 2,413,440 Farrington Dec. 31, 19462,474,040 Day June 21, 1949 2,529,547 Fisher Nov. 1-4, 1950 2,567,845Hoagland Sept. 11, 1951 2,573,150 Lacy Oct. 30, 1951 2,619,618 AdlerNov. 25, 1952 2,641,694

' Hallmark June 9, 1953

